Bowman’s capsule

Figure 19.1 The nephron. The functional unit of the kidney is the nephron, which has two components. The vascular component includes the afferent arteriole, which carries blood toward the glomerulus where filtration of the plasma takes place. The efferent arteriole carries the unfiltered blood away from the glomerulus. The tubular component of the nephron includes Bowman s capsule, which receives the filtrate the proximal tubule the Loop of Henle and the distal tubule. The tubule processes the filtrate, excreting waste products and reabsorbing nutrient molecules, electrolytes, and water.

Upon leaving the glomerular capillaries, the filtrate enters the first portion of the tubule, Bowman s capsule. The glomerulus is pushed into Bowman s capsule, much like a fist pushed into a balloon or a catcher s mitt. From Bowman s capsule, the filtrate passes through the proximal tubule,... 

Figure 19.2 Basic renal processes. These processes include filtration, reabsorption, and secretion. (1) Filtration is the movement of fluid and solutes from the glomerular capillaries into Bowman s capsule. (2) Reabsorption, which takes place throughout the nephron, is the movement of filtered substances out of the tubule and into the surrounding peritubular capillaries. (3) Secretion is the movement of selected unfiltered substances from the peritubular capillaries into the renal tubule for excretion. Any substance that is filtered or secreted, but not reabsorbed, is excreted in the urine.

The first step in the formation of urine is glomerular filtration. The barrier to filtration is designed to facilitate the movement of fluid from the glomerular capillaries into Bowman s capsule without any loss of cellular elements or plasma proteins. Maximizing GFR has two advantages ... 

The basement membrane is an acellular meshwork consisting of collagen and glycoproteins. The collagen provides structural support and the negatively charged glycoproteins prevent the filtration of plasma proteins into Bowman s capsule. 

The inner wall of Bowman s capsule consists of specialized epithelial cells referred to as podocytes. This layer of epithelial cells is not continuous instead, the podocytes have foot-like processes that project outward. The processes of one podocyte interdigitate with the processes of an adjacent podocyte, forming narrow filtration slits. These slits provide an ample route for the filtration of fluid. 

Bowman s capsule pressure (PBC) is a hydrostatic pressure generated by the presence of filtered fluid within Bowman s capsule. This pressure pushes the fluid out of the capsule and forward toward the remainder of the renal tubule for processing. Bowman s capsule pressure also tends to oppose filtration. On average, PBC is approximately 15 mmHg. 

Blood is supplied to the kidneys via the renal vein, a branch of the descending vena cava, at relatively high pressure to ensure rapid filtration of plasma across the membranes of the blood vessels in the glomeruli and the epithelial cells of the Bowman s capsule. The net filtration pressure of about 5-6 kPa, is the difference between the blood pressure forcing plasma water across the filtration barrier and the opposing osmotic and... 

The main filtering units of the kidneys are called nephrons-, about one million nephrons are present in each kidney. Each nephron consists of a renal corpuscle and a unit called a tubule. Blood carrying normal metabolic wastes such as urea and creatine moves through a portion of the corpuscle called the glomerulus, where a filtrate forms that contains water, normal metabolic products, and also waste products the filtrate collects in another unit called Bowman s capsule. Glomerular filtrate then moves into a highly convoluted and multifaceted set of tubes - the tubule - where most useful products (water, vitamins, some minerals, glucose, amino acids) are taken back into the blood, and from which waste products are collected as urine. The relative amounts of water and minerals secreted or returned to the blood are under hormonal control. 

A plethora of methods has been developed to evaluate renal function by dynamic renography and remote analysis of the excretion of renal function markers. The underlying principle is that the kidneys excrete a majority of small hydrophilic molecules and their clearance, secretion, or fixation in the kidney is quantifiable. When a renal marker in plasma is filtered through the glomeruli, the accumulation of the filtrate in the Bowman s capsule. One or more of the following events may occur in the renal tubule once a marker is filtered or is in plasma [171] ... 

The smallest functional unit of the kidney is the nephron. In the glomerular capillary loops, ultrafiltration of plasma fluid into Bowman s capsule (BC) yields primary urine. In the proximal tubules (pT), approx. 70% of the ultrafiltrate is retrieved by isoosmotic reabsorption of NaCl and water. In the thick portion of the ascending limb of Henle s loop (HL), NaCl is absorbed unaccompanied by water. This is the prerequisite for the hairpin countercurrent mechanism that allows build-up of a very high NaQ concentration in the renal medulla In the distal tubules (dT), NaCl and water are again jointly reabsorbed. At the end of the nephron, this process involves an aldosterone-controlled exchange of Na+ against 1C or H. In the collecting tubule (C), vasopressin (antidiuretic hormone, ADH) increases the epithelial permeability for water, which is drawn into the hyperosmolar milieu of the renal medulla and thus retained in the body. As a result, a concentrated urine enters the renal pelvis. 

The functional unit of the kidney is the nephron. It is made up of the Malpighian bodies or renal corpuscles (consisting of Bowman s capsules and the glomerulus), the proximal tubule, Henle s loop, and the distal tubule, which passes into a collecting duct. The human kidney contains around one million nephrons. The nephrons form urine in the following three phases. 

Both the medulla and the cortex of the kidney synthesize prostaglandins, the medulla substantially more than the cortex. COX-1 is expressed mainly in cortical and medullary collecting ducts and mesangial cells, arteriolar endothelium, and epithelial cells of Bowman s capsule. COX-2 is restricted to the renal medullary interstitial cells, the macula densa, and the cortical thick ascending limb. 

WT1 is present in the metanephric mesenchyme before induction and is upregulated during induction. Blocking induction stops the production of WT1. WT1 is expressed at high levels during the condensation of the mesenchyme and its transition to epithelium. Its expression diminishes thereafter, except in the podocyte layer of Bowman s capsule. WT1 knockout mice do not develop kidneys. The metanephric mesenchyme from these mice cannot be induced by wild-type inducers. 

The rest of the S-shaped tubule retains its epithelial character and segments into proximal tubule, loop of Henle and distal tubule. The cells lose expression of WT1, PAX-2 and n-MYC. Capillaries grow into the cleft in Bowman s capsule. These apparently arise from blood vessels in response to angiogenic factors from the nephron. One such factor is VEGF, known to be secreted by early nephrons. 

Intermediate-duration gavage exposure to a higher FireMaster FF-1 dose of 30 mg/kg/day for 4.5 weeks caused dilation of Bowman s capsule with serous fluid in rats observed for 60 days posttreatment (Gupta and Moore 1979) however, rats that were similarly treated (< 30 mg/kg/day for 30 days) but observed longer (90 days posttreatment) had normal kidney histology, urinalysis values, and BUN (Gupta et al. 

Glomureli are the fine blood vessels entering and leaving the Bowman s capsule that is part of the kidneys filtration unit, called nephron. 

The operation of the human kidney simulated by hemodialyzers is illustrated in Figure 12.1. The process begins in the glomerulus, a network of tiny capillaries surrounding spaces called Bowman s capsules. Blood flowing through these... 

Figure 12.1 Schematic of a single nephron, the functional unit of the kidney. Microsolutes are filtered from blood cells in Bowman s capsules. As the filtrate passes towards the collection tubule most of the microsolutes and water are reabsorbed by a type of facilitated transport process. The fluid finally entering the collecting tubule contains the nitrogenous wastes from the body and is excreted as urine. There are about 1 million nephrons in the normal kidney [1]...

Glomerulus A functional unit of the mammalian kidney consisting of a small bunch of capillaries projecting into a capsule (Bowman s capsule), which serves to collect the filtrate from the blood of those capillaries and direct it into the kidney tubule. 

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